diff --git a/src/compiler/program.gleam b/src/compiler/program.gleam
index 4c3bb7f..58fd89d 100644
--- a/src/compiler/program.gleam
+++ b/src/compiler/program.gleam
@@ -5,17 +5,19 @@
 //// filesystem. 
 //// It does not write to the filesystem.
 
-import compiler/python
 import errors
+import filepath
 import glance
 import gleam/dict
 import gleam/list
 import gleam/result
-import pprint
 import simplifile
 
 pub type GleamProgram {
-  GleamProgram(modules: dict.Dict(String, glance.Module))
+  GleamProgram(
+    source_directory: String,
+    modules: dict.Dict(String, glance.Module),
+  )
 }
 
 pub type CompiledProgram {
@@ -24,9 +26,22 @@ pub type CompiledProgram {
 
 /// Load the entry_point file and recursively load and parse any modules it
 ///returns.
-pub fn load_program(entry_point: String) -> Result(GleamProgram, errors.Error) {
-  GleamProgram(modules: dict.new())
-  |> load_module(entry_point)
+pub fn load_program(
+  source_directory: String,
+) -> Result(GleamProgram, errors.Error) {
+  source_directory
+  |> simplifile.is_directory
+  |> result.map_error(errors.FileOrDirectoryNotFound(source_directory, _))
+  |> result.try(fn(_) { find_entrypoint(source_directory) })
+  |> result.try(load_module(GleamProgram(source_directory, dict.new()), _))
+}
+
+pub fn find_entrypoint(source_directory: String) -> Result(String, errors.Error) {
+  let base_name = filepath.base_name(source_directory)
+  let entrypoint = base_name <> ".gleam"
+  simplifile.is_file(filepath.join(source_directory, entrypoint))
+  |> result.replace(entrypoint)
+  |> result.map_error(errors.FileOrDirectoryNotFound(entrypoint, _))
 }
 
 /// Parse the module and add it to the program's modules, if it can be parsed.
@@ -35,12 +50,12 @@ fn load_module(
   program: GleamProgram,
   module_path: String,
 ) -> Result(GleamProgram, errors.Error) {
-  pprint.debug(module_path)
   case dict.get(program.modules, module_path) {
     Ok(_) -> Ok(program)
     Error(_) -> {
       let module_result =
         module_path
+        |> filepath.join(program.source_directory, _)
         |> simplifile.read
         |> result.map_error(errors.FileReadError(module_path, _))
         |> result.try(parse(_, module_path))
@@ -81,9 +96,8 @@ fn add_module(
   module_path: String,
   module_contents: glance.Module,
 ) -> GleamProgram {
-  GleamProgram(modules: dict.insert(
-    program.modules,
-    module_path,
-    module_contents,
-  ))
+  GleamProgram(
+    ..program,
+    modules: dict.insert(program.modules, module_path, module_contents),
+  )
 }
diff --git a/src/errors.gleam b/src/errors.gleam
index e602719..e91b337 100644
--- a/src/errors.gleam
+++ b/src/errors.gleam
@@ -3,16 +3,23 @@ import internal/errors as internal
 import simplifile
 
 pub type Error {
-  FileReadError(module: String, error: simplifile.FileError)
-  FileWriteError(module: String, error: simplifile.FileError)
+  FileOrDirectoryNotFound(path: String, error: simplifile.FileError)
+  FileReadError(path: String, error: simplifile.FileError)
+  FileWriteError(path: String, error: simplifile.FileError)
+  DeleteError(path: String, error: simplifile.FileError)
+  MkdirError(path: String, error: simplifile.FileError)
   GlanceParseError(error: glance.Error, module: String, contents: String)
 }
 
 pub fn format_error(error: Error) -> String {
   case error {
+    FileOrDirectoryNotFound(filename, _) ->
+      "File or directory not found " <> filename
     FileReadError(filename, simplifile.Enoent) -> "File not found " <> filename
     FileReadError(filename, _) -> "Unable to read " <> filename
     FileWriteError(filename, _) -> "Unable to write " <> filename
+    DeleteError(filename, _) -> "Unable to delete " <> filename
+    MkdirError(filename, _) -> "Unable to mkdir " <> filename
     GlanceParseError(error, filename, contents) ->
       internal.format_glance_error(error, filename, contents)
   }
diff --git a/src/macabre.gleam b/src/macabre.gleam
index 2bc0b09..a3b2507 100644
--- a/src/macabre.gleam
+++ b/src/macabre.gleam
@@ -2,56 +2,47 @@ import argv
 import compiler
 import compiler/program
 import errors
+import filepath
+import gleam/dict
 import gleam/io
 import gleam/result
-import gleam/string
-import internal/errors as error_functions
 import output
-import pprint
-import simplifile
 
 pub fn usage(message: String) -> Nil {
   io.println("Usage: macabre <filename.gleam>\n\n" <> message)
 }
 
-fn compile_module(filename: String) -> Result(Nil, String) {
-  simplifile.read(filename)
-  |> result.replace_error("Unable to read '" <> filename <> "'")
-  |> result.try(fn(content) {
-    content
-    |> compiler.compile
-    |> result.map_error(error_functions.format_glance_error(
-      _,
-      filename,
-      content,
-    ))
-  })
-  |> result.try(output.write(_, output.replace_extension(filename)))
+fn write_program(
+  program: program.CompiledProgram,
+  build_directory: String,
+) -> Result(Nil, errors.Error) {
+  build_directory
+  |> output.delete
+  |> result.try(fn(_) { output.create_directory(build_directory) })
+  |> result.try(fn(_) { output.write_prelude_file(build_directory) })
   |> result.try(fn(_) {
-    // TODO: eventually, this has to be output to a base directory,
-    // not one copy per module.
-    filename
-    |> output.replace_file("gleam_builtins.py")
-    |> output.write_prelude_file
+    dict.fold(program.modules, Ok(Nil), fn(state, name, module) {
+      result.try(state, fn(_) {
+        build_directory
+        |> filepath.join(name)
+        |> output.replace_extension()
+        |> output.write(module, _)
+      })
+    })
   })
 }
 
 pub fn main() {
   case argv.load().arguments {
     [] -> usage("Not enough arguments")
-    [input] ->
-      case string.ends_with(input, ".gleam") {
-        False -> usage(input <> ":" <> " Not a gleam input file")
-        True -> {
-          input
-          |> program.load_program
-          |> result.map(compiler.compile_program)
-          |> result.try(output.write_program(_, "build"))
-          |> result.map_error(output.write_error)
-          |> result.unwrap_both
-          // both nil
-        }
-      }
+    [directory] ->
+      directory
+      |> program.load_program
+      |> result.map(compiler.compile_program)
+      |> result.try(write_program(_, filepath.join(directory, "build/")))
+      |> result.map_error(output.write_error)
+      |> result.unwrap_both
+    // both nil
     [_, _, ..] -> usage("Too many arguments")
   }
 }
diff --git a/src/output.gleam b/src/output.gleam
index a34278e..e1b7efa 100644
--- a/src/output.gleam
+++ b/src/output.gleam
@@ -1,4 +1,3 @@
-import compiler/program
 import errors
 import filepath
 import gleam/io
@@ -11,7 +10,7 @@ pub fn write(contents: String, filename: String) -> Result(Nil, errors.Error) {
   |> result.map_error(errors.FileWriteError(filename, _))
 }
 
-fn replace_extension(filename: String) -> String {
+pub fn replace_extension(filename: String) -> String {
   filename |> filepath.strip_extension <> ".py"
 }
 
@@ -33,17 +32,12 @@ pub fn compile_result(filename: String, result: Result(Nil, String)) -> Nil {
   }
 }
 
-pub fn write_prelude_file(filepath: String) -> Result(Nil, String) {
-  filepath
-  |> simplifile.write(python_prelude.gleam_builtins)
-  |> result.replace_error("Unable to write prelude")
-}
+pub fn write_prelude_file(build_directory: String) -> Result(Nil, errors.Error) {
+  let full_path = filepath.join(build_directory, "gleam_builtins.py")
 
-pub fn write_program(
-  program: program.CompiledProgram,
-  directory: String,
-) -> Result(Nil, errors.Error) {
-  todo
+  full_path
+  |> simplifile.write(python_prelude.gleam_builtins)
+  |> result.map_error(errors.FileWriteError(full_path, _))
 }
 
 pub fn write_error(error: errors.Error) -> Nil {
@@ -51,3 +45,12 @@ pub fn write_error(error: errors.Error) -> Nil {
   |> errors.format_error
   |> io.println
 }
+
+pub fn delete(path: String) -> Result(Nil, errors.Error) {
+  simplifile.delete_all([path]) |> result.map_error(errors.DeleteError(path, _))
+}
+
+pub fn create_directory(path) -> Result(Nil, errors.Error) {
+  simplifile.create_directory(path)
+  |> result.map_error(errors.MkdirError(path, _))
+}